1. Technical Field
The present invention relates to an image system.
2. Related Art
A time-of-flight camera (TOF camera) is a camera system that creates distance data with the time-of-flight (TOF) principle. The simplest version of a time-of-flight camera uses light pulses. The illumination is switched on for a very short time, and the generated light pulse illuminates the scene and is reflected by the objects. The camera lens gathers the reflected light, forming images onto the sensor plane. Depending on the distances, the incoming light may experience a delay. The camera has photo diodes (PDs), which convert incoming light into currents. In analog timing imagers, connected to the photo diode are fast switches, which direct the current to one of plural memory elements (e.g. a capacitor). In digital timing imagers, a time counter, running at several gigahertz, is connected to each photo detector and stops counting when light is sensed.
In an analog timer, a PD pixel uses two switches and two memory elements. The switches are controlled by a pulse with the same length as the light pulse, where the control signal of one switch is delayed by exactly the pulse width. Depending on the delay, different amounts of electrical charge are respectively stored in the two memory elements. The distance from the camera to the object can be estimated by comparing the amounts of electrical charge stored in the two memory elements.
Light generated for being sensed by TOF cameras illuminates the complete scene. Light may go through different paths before it arrives at the object, causing the estimated distance to be greater than the actual distance.